1. Field of the Invention
The invention relates to a method and a device for specifying a boost control strategy of a hybrid vehicle drive.
2. Description of the Related Art
Hybrid drives have been on the market for a number of years as a fuel-saving and more environmentally-friendly alternative to the conventional internal combustion engine. The hybrid drive generally is defined as having at least two different energy converters and two different energy stores.
The converters generally are an internal combustion engine and an electric motor. The energy store for the internal combustion engine generally is a combustible fuel and the energy store for the electric motor generally is a battery, a capacitor or a flywheel.
A hybrid vehicle has an advantage over conventional vehicles with internal combustion engines that the hybrid vehicle can recover most of the braking energy (with the exception of the efficiency losses). The recovered or recuperated braking energy is buffered in the battery of the electric motor, with the electric motor functioning as a mechanical-electrical converter.
The buffering of the energy, that is to say the recuperation, takes place during active braking and in the overrun mode. The overrun mode is a vehicle state in which the internal combustion engine is not actively driving the vehicle because the driver has released the accelerator pedal. The vehicle is thus in a passive state and is propelled only by its own inertial mass, until the various driving resistances gradually decelerate the vehicle until it comes to a halt. The supply of gasoline and the ignition are deactivated in hybrid vehicles during the overrun phase. Furthermore, technical measures are taken to prevent engine braking by the internal combustion engine in the overrun mode and hence to allow the kinetic energy to be made available as completely as possible to the electric motor, which is configured as a mechanical-electrical converter.
A kinetic energy recovery system (KERS) recently has been used in automobile racing to recover kinetic energy. The stored energy is used to operate the electric motor for a short time on demand, such that the power of the electric motor can be used in addition to the main motor, the internal combustion engine, in acceleration phases. These phases in which the main motor is assisted by an electric motor are referred to as boost phases. The storable maximum energy quantity available for boosting for the electric motor is limited, for example to 500 kJ.
In the mechanical variant for the energy store of the electric motor, in a vacuum cylinder, a flywheel system that rotates at up to 64,000 rpm is accelerated by the braking process, and later can impart the stored energy back to the drive axle via a continuously variable gearing. Such an energy recovery system is disclosed for example in WO 2009/141646 A1.
It is an object of the present invention to provide an improved method and an improved device for specifying a boost control strategy of a hybrid vehicle drive to make it possible to utilize the maximum available energy quantity in an efficient manner.